1. Field of the Invention
The present invention relates generally to shunts, and more particularly to shunts for syrinx cavity drainage and associated procedures, including percutaneous introduction and deployment.
2. Description of Related Art
Syringomyelia is a condition in which a cyst forms within the spinal cord, and is filled with fluid essentially identical with CerebroSpinal Fluid (CSF). Syringomyelic cavities are generally thought to develop when there is a partial obstruction to the circulation of CSF within the subarachnoid space, thereby causing migration of fluid through the substance of the spinal cord for collection within the spinal cord. Dynamic relationships of CSF pulsatiltity and physiological transient pressure changes cause the fluid cavity within the cord to become distended and to expand in an upward and/or downward direction, thereby destroying spinal cord tissue and impairing spinal cord function, resulting in permanent damage. In extreme situations, the damage may take the form of paraplegia or quadriplegia. Other symptoms include pain, numbness, weakness, disruption in temperature sensation, adverse effects on sweating, sexual function, and bladder and bowel control.
The referenced (partial) obstruction may derive from an abnormality of the brain called an Arnold-Chiari malformation, where the lower part of the cerebellum protrudes from its normal location at the back of the head into the cervical portion of the spinal canal. Syringomyelia may also occur as a result of complications from trauma, meningitis, hemorrhaging, a tumor, or arachnoiditis.
As reported in Batzdorf, et al., “A Clinical Appraisal of Syrinx Cavity Shunting Procedures,” J Neurosurg 89:382-388, 1998, Chiari-related syringomyelia is generally considered to be best treated by eliminating the partial block by suboccipital decompression. Likewise, spinal decompression and arachnoid scar resection, with placement of a dural graft is recommended in appropriate cases of primary spinal syringomyelia when the obstruction to CSF flow is very limited to a narrow area. In any case, the primary goal is one of reestablishing unrestricted subarachnoid CSF flow.
Some conditions, however, do not lend themselves to the treatment approaches referred to above. For example, in many instances of syringomyelia that develop after spinal cord injury, the scar tissue surrounding the spinal cord is not limited to a narrow, more easily treatable band, but instead extends circumferentially around the cord and over several vertebral segments. Problematic diffuse arachnoid scarring is also seen after meningitis and in some patients following subarachnoid hemorrhage. In these cases, shunt placement presents a viable treatment option, and is often the only available treatment.
It is to be appreciated that existing shunt devices used in humans present an approximately 50% failure rate. Batzdorf, et al. further reports on several failure modes for existing devices. Shunt obstruction is the most common of these failure modes. In existing devices that provide drainage through a port, or ports, only at the tip of the device, collapse of the syrinx cavity can terminate proper function. In other devices in which lateral drainage holes are provided, tissue in-growth has also been observed. In-growth of glial tissue may make it impossible to withdraw a shunt tube during attempted revision, thereby resulting in further complications. In a T-shaped device, with one arm directed upward into the cavity, and the other arm downward, in-situ rotation of the device risked spinal cord injury.
After some considerable time since reporting the failure modes, no adequate alternative has yet been made available to physicians to treat the patient population in need.